Synthetic Biologics and Enterome Bioscience Collaborate on Microbiome Research to Support Synthetic Biologics' C. difficile Program

Synthetic Biologics, Inc. (NYSE MKT: SYN), a developer of novel anti-infective biologic and drug candidates targeting specific pathogens that cause serious infections and diseases, and Enterome Bioscience SA, a pioneer in the development of innovative disease management solutions based on a deep understanding of the gut microbiome, today announced that they have entered into an agreement to conduct metagenomic research on the effects of beta-lactam antibiotics on the gastrointestinal microflora (microbiome) of human patients. As part of this collaboration, a clinical microbiome study of approximately 100 patients is expected to begin next month. Research findings should provide important insights as Synthetic Biologics advances the development of SYN-004, which is intended to protect the gut microbiome from the effects of intravenous (IV) beta-lactam antibiotics, and in particular to prevent C. difficile(C. diff) infections. Phase Ia and Ib clinical trials of Synthetic Biologics' SYN-004 are scheduled to begin later this year.

The Enterome microbiome study, scheduled for completion in the second half of 2014, is expected to provide a better understanding of the harmful effects of beta-lactam antibiotics on the gut bacterial community. The goal is to establish a "fingerprint" of the damage caused by beta-lactam antibiotics, thus yielding a panel of bacterial biomarkers that can be leveraged for diagnostic purposes. This novel study should clearly define the impact of beta-lactam antibiotics on the natural bacterial diversity of the gut microbiome. Changes in the gut microbiome have been related to multiple diseases, including C. diff infections, antibiotic-associated diarrhea, obesity, diabetes and other metabolic diseases. This study will utilize Enterome's state-of-the-art shotgun metagenomic sequencing technology to profile the human gut microbiome.

"We are pleased to establish this collaboration with Enterome, a pioneer in the development of biomarkers and therapies for diseases of the gut microbiome," stated Jeffrey Riley, CEO of Synthetic Biologics. "Findings from this study should support our C. diff therapeutic program, which focuses on protecting and maintaining the balance of bacterial microflora in the gut, while also establishing our presence in Europe."

Synthetic Biologics' lead anti-infective product candidate, SYN-004, is the first therapy designed to neutralize IV antibiotics in the gut, and is intended to protect and maintain the balance of bacterial flora in the gastrointestinal tract, to prevent the devastating effects of C. diff. The U.S. Centers for Disease Control and Prevention (CDC) has classified C. diff as an "urgent public health threat"[i], surpassing Methicillin-resistant Staphylococcus aureus (MRSA) as the number one hospital-acquired infection in the United States. C. diff is a multidrug-resistant bacterium that infects 1.1 million U.S. patients annually[ii]. In the U.S., patients with C. diff are hospitalized an estimated 3.6-7 extra days[iii], costing more than $8.2 billion[iv].

"The signing of this agreement with Synthetic Biologics is another important corporate milestone for Enterome. I am very pleased that our pioneering approach to understanding the linkage between changes in the gut microbiome and disease has convinced Synthetic Biologics to work with us on such an important personalized medicine project. It is clear that new diagnostic solutions are needed to properly address the growing problem of antibiotic-induced dysbiosis and associated hospital-acquired bacterial infections," stated Pierre Belichard, CEO of Enterome. "Tailoring the use of anti-infective treatments based on microbiome profiling is beginning to show great promise as a way to address the management of infectious diseases."

"Comparing Enterome's technology to other genomic analyses of gut microbiome is like comparing a Quad Full High definition color resolution TV to resolution of an analog black & white TV," added Mr. Riley.

About SYN-004 Clinical Development

Synthetic Biologics is developing SYN-004, a novel second generation oral enzyme drug candidate, to be co-administered with commonly used IV beta-lactam antibiotics and is intended to protect the gastrointestinal microflora (microbiome) from the harmful effects of such antibiotics, thus potentially preventing C. diff infections. Planned next steps for SYN-004 include: 1) initiation of a 28-day bridging toxicology study in June 2014; 2) filing of an Investigational New Drug (IND) application to initiate Phase Ia and Ib clinical trials in the second half of 2014, with preliminary topline data expected by year-end 2014; and, 3) initiation of a Phase II efficacy study is expected to begin in the first half of 2015.

About Enterome Bioscience SA

Enterome is pioneering the development of innovative disease management solutions based on a deep understanding of the gut microbiome. Understanding and modifying the changes that occur in the gut microbiome during disease and in response to therapeutic interventions represent an entirely new and untapped opportunity to impact medicine.

Initially Enterome is using its expertise and proprietary technologies to develop novel diagnostic products to support patient stratification, personalized therapies and the clinical development of new drugs for the treatment of microbiome-related diseases such as inflammatory bowel diseases and metabolic diseases (diabetes and obesity). Enterome's unique Metagenotyping process has allowed it to develop biomarkers for treatment response prediction, disease activity monitoring and as potential companion diagnostics.

The company was established in 2012 in Paris, France, and has raised a total of 17.5m from leading venture capital investors (Seventure, Omnes Capital & Lundbeckfond Ventures) and two strategic investors (Danone & Shire).

Synthetic Biologics, Inc. (NYSE MKT: SYN) is a biotechnology company focused on the development of novel anti-infective biologic and drug candidates targeting specific pathogens that cause serious infections and diseases. The Company is developing an oral biologic to protect the gastrointestinal microflora from the effects of IV antibiotics for the prevention of Clostridium difficile (C. difficile) infection, an oral treatment to reduce the impact of methane producing organisms on constipation-predominant irritable bowel syndrome (C-IBS), a series of monoclonal antibodies for the treatment of Pertussis and Acinetobacter infections, and a biologic targeted at the prevention and treatment of a root cause of a subset of IBS. In addition, the Company is developing an oral estriol drug for the treatment of relapsing-remitting multiple sclerosis (MS) and cognitive dysfunction in MS. For more information, please visit Synthetic Biologics' website at http://www.syntheticbiologics.com.

This release includes forward-looking statements on Synthetic Biologics' current expectations and projections about future events. In some cases forward-looking statements can be identified by terminology such as "may," "should," "potential," "continue," "expects," "anticipates," "intends," "plans," "believes," "estimates," and similar expressions. These statements are based upon current beliefs, expectations and assumptions and are subject to a number of risks and uncertainties, many of which are difficult to predict and include statements regarding, the anticipated timing and results of the Synthetic Biologics' clinical trials, studies and development efforts and the expected benefits of SYN-004. The forward-looking statements are subject to risks and uncertainties that could cause actual results to differ materially from those set forth or implied by any forward-looking statements. Important factors that could cause actual results to differ materially from those reflected in Synthetic Biologics' forward-looking statements include, among others, a failure to receive the necessary regulatory approvals for commercialization of Synthetic Biologics' therapeutics, a failure of Synthetic Biologics' clinical trials, studies and those conducted by investigators, to be commenced or completed on time or to achieve desired results, a failure of Synthetic Biologics' clinical trials to receive anticipated funding, a failure of Synthetic Biologics' candidates for the prevention and treatment of infectious diseases to be successfully developed or commercialized, Synthetic Biologics' inability to maintain its licensing agreements, or a failure by Synthetic Biologics or its strategic partners to successfully commercialize products and other factors described in Synthetic Biologics' report on Form 10-K for the year endedDecember 31, 2013and any other filings with the SEC. The information in this release is provided only as of the date of this release, and Synthetic Biologics undertakes no obligation to update any forward-looking statements contained in this release on account of new information, future events, or otherwise, except as required by law.

ii. This information is an estimate derived from the use of information under license from the following IMS Health Incorporated information service: CDM Hospital database for full year 2012. IMS expressly reserves all rights, including rights of copying, distribution and republication.